Idaho semi-weekly world. [volume] (Idaho City, Idaho Territory) 1875-1908, 1887-11-22
GATHERING THE GOLD.
"sthods Adopted for Getting the Meta,
out OF the Free Milling Ore

A""p.on TOR Settfng the Metal
Out OF the Free Milling Ore.
At breckenridge, Col. the other day.
saw the Jumbo stamp-mill, and there
got 1air insight into the method of
getting the gold out Of what il called
free milling ore. The stuff that comes
from the mine is first put through a
crusher. which breaks it up fine, and
the product is then run through rollers
which pulverizes it. though. perhaps.
coarsely From the rollers It falls to
the lower floor, upon which the NOR
tars are located. At the Jumbo mill
the dirt Is fed to the stamps by hand:
In other mills it falls through chutes
which work automatically, and never
1eeu more than is necessary at a
time. The stamps are arranged In
batteries OF five stamps each. They
work up and down in oak easements,
and their motions are regulated by
cams on shaft geared to the motive
machinery. The stamps weigh from
400 to 900 pounds, according to the
character of the ore treated. Water
flows into the mortars and out of them
down tables to the waste fumes which
carry the refuse away. Stamps in this
country run as low as thirty drops a
minute. and seldom over sixty; in
California they drop seventy to 100
times a minute. The two kinds of mills
are distinguished by the rapidity or
slowness of their drops. and those used
here are all built by Peter Mcfarland,
and are called Gilpin County mills,
from Netherlands home place, which
Is in Gilpin County. while the others
are known as California mills. They
cost from $3.50 for five-stamp pros
pecting mill to 100000 for a 100-stamp
mill. The dirt being fed into the mortars
is pounded and pounded by the stamps;
the silica, porphyry and other refuse
is carried off by the water, but the gold
Is caught by two copper plates coated
with quicksilver that line the sides of
the mortar; any Of the precious metal
that escapes from the mortar may be
caught on the 4x8 feet copper plates
that are quicksilver coated and lie on
the table over which the refuse is car.
ried. Some of the gold gets away, OF
course, but the Jumbo saves as much
as 80 per cent of its gold. and McFar-
land is now building mills which he
claims will save 50 per cent. of the as
sayed value of ore.
Concentrations are used whore the ore
is too low grade to pay for smelling in
its crude state. By concentrating SIC
nrS ha 81 I.
mill product, which will represent six
or seven tons in ore, may be worth SIC
to $50 per ton. The scheme is very
simple. The crushed and rolled ore i.
fed through chutes to revolving screens
ranging in size from three fourths inch
openings to one-eighth. Each of these
screens has trough and chute which
feeds a jig box. The jig boxes work OF
an eccentric and keep up a spasm-likt
motion. There is a screen in each abou
six inches from the top, and this screer
is covered with lead or other heavy
ore material. which prevents thu
| silica, porphyry and other light stuf
from going through. The motion
shakes the metal to the bottom of tn
| boxes, where it remains until valves il
the bottom are opened and the concen
trates are removed. This machine, lik,
all the others called by different names
and known as triumps, frue vanners
bubbles. bump plates. etc, is an appli
cation of the well-known law of specifi,
gravity; the heaviest material falls t.
the bottom in all these machines, ant
the light stuff goes dancing away oil
the water. The bump plate. which i
claimed to be new invention by Pete
Mcfarland, is large steel plate set a
an incline of few degrees; the ore i
fed to the lower part of the place from
water trough. and as the high en'
bumps it carries forward and up owe
the top of the plate the heavy concen
trates. Cor. 81. Louis Globe Democrat